[feat] Serial output

include/serial.h

@@ -0,0 +1,15 @@
+#pragma once
+
+#include <efi.h>
+#include <efiser.h>
+
+struct serial_context {
+    EFI_SERIAL_IO_PROTOCOL *SerialIo;
+};
+
+extern serial_context g_serial;
+
+void serial_init(EFI_SERIAL_IO_PROTOCOL *SerialIo);
+void serial_write(const char *str);
+void serial_write_char(char c);
+char serial_read_char();